Diagnostic Accuracy of Body Mass Index to Identify Obesity in Older Adults: NHANES 1999–2004
Published Date:Dec 01 2015
Source:Int J Obes (Lond). 40(5):761-767.
Pubmed Central ID:PMC4854777
Funding:U48 DP005018/DP/NCCDPHP CDC HHS/United States
Body composition changes with aging lead to increased adiposity and decreased muscle mass, making the diagnosis of obesity challenging. Conventional anthropometry, including body mass index (BMI), while easy to use clinically may misrepresent adiposity. We determined the diagnostic accuracy of BMI using dual energy x-ray absorptiometry (DEXA) in assessing the degree of obesity in older adults.
The National Health and Nutrition Examination Surveys 1999–2004 were used to identify adults aged ≥60years with DEXA measures. They were categorized (yes/no) as having elevated body fat by gender (men≥25%; females ≥35%) and by body mass index (BMI) ≥25 and ≥30kg/m2. The diagnostic performance of BMI was assessed. Metabolic characteristics were compared in discordant cases of BMI/body fat. Weighting and analyses were performed per NHANES guidelines.
We identified 4,984 subjects (men:2,453; female:2,531). Mean BMI and % body fat was 28.0kg/m2 and 30.8% in men, and 28.5kg/m2 and 42.1% in females. A BMI ≥30kg/m2 had a low sensitivity and moderately high specificity (men:32.9% and 80.8%, concordance index 0.66; females:38.5% and 78.5%, concordance 0.69) correctly classifying 41.0 and 45.1% of obese subjects. A BMI ≥25kg/m2 had a moderately high sensitivity and specificity (men:80.7% and 99.6%, concordance 0.81;females:76.9% and 98.8%, concordance 0.84) correctly classifying 80.8 and 78.5% of obese subjects. In subjects with BMI<30kg/m2 body fat was considered elevated in 67.1% and 61.5% of males and females, respectively. For a BMI≥30kg/m2, sensitivity drops from 40.3 to 14.5% and 44.5 to 23.4%, while specificity remains elevated (>98%),in males and females, respectively in those 60–69.9years to subjects aged ≥80years. Correct classification of obesity using a cutoff of 30kg/m2 drops from 48.1 to 23.9% and 49.0 to 19.6%, in males and females in these two age groups.
Traditional measures poorly identify obesity in the elderly. In older adults, BMI may be a suboptimal marker for adiposity.
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